The present invention relates to an illuminating device formed of a flexible light guide for combination with a light source. The light guide comprises a flexible hollow tube closed at its ends and made of a plastics material, which has a predetermined index of refraction, and a light conducting liquid, which fills the flexible tube and whose refractive index is greater than that of the plastics material.
The term "light" is to be understood to mean electromagnetic radiation in the ultra-violet (UV), visible and infrared (IR) spectral ranges.
One aim of the present invention is to provide an illuminating device of the initially mentioned type which makes it possible to illuminate an object with relatively intense light and more particularly with light in the near ultra-violet and visible spectral ranges, though the invention is not to be restricted exclusively to these ranges. In particular it is an aim of the invention to provide an illuminating device which has the following advantageous properties:
A. The illuminating device is to be capable of providing an output radiative power or energy of up to several watts in continuous operation;
B. THE ILLUMINATING DEVICE IS TO BE CAPABLE OF PROLONGED USE WITHOUT DETERIORATING, THAT IS TO SAY ITS EFFICIENCY IS NOT TO BE IMPAIRED EITHER BY INTENSIVE RADIATION, MORE PARTICULARLY ULTRA-VIOLET RADIATION, NOR BY EXTENDED PERIODS OF OPERATION OR OF STORAGE;
C. THE ILLUMINATING DEVICE IS TO BE COMPACT AND ECONOMIC IN CONSTRUCTION AND SHOULD BE CAPABLE OF BEING USED WITH LIGHT SOURCES WHICH ARE CHEAP TO PURCHASE AND TO OPERATE, THAT IS TO SAY MORE PARTICULARLY WITH METAL VAPOR (FOR EXAMPLE MERCURY) OR XENON HIGH PRESSURE LAMPS OR TUNGSTEN-HALOGEN INCANDESCENT LAMPS;
D. THE ILLUMINATING DEVICE SHOULD BE CAPABLE OF BEING EASILY MANIPULATED SO THAT IT IS POSSIBLE TO USE IT EVEN FOR ILLUMINATING OBJECTS WHICH ARE DIFFICULT OF ACCESS; AND
E. THE LIGHT INLET ANGLE AND THE TRANSMISSION OF THE LIGHT GUIDE OF THE ILLUMINATING DEVICE SHOULD BE AS LARGE AS POSSIBLE.
An illuminating device with these properties is required for example in dentistry for polymerisation of synthetic resin fillings with ultra-violet light, for diagnostic purposes and for treatment purposes, and also for endoscopic purposes for illumination and treatment.
The previously proposed illuminating devices of the initially mentioned type all leave to be desired in one particular or another respect. Illuminating devices with fiber bundle light guides are, owing to the necessary cementing of the fiber bundle ends, not in a position to transmit high radiative powers or energies and more particularly in the ultra-violet spectral range suffer from a low efficiency.
Illuminating devices with a flexible light guide comprising a single thin quartz fiber must use an expensive laser as a light source, since such light guides cannot transmit radiation from divergent surface radiators or sources, as is the case with a high pressure mercury lamp.
Previously proposed illuminating devices with a flexible light guide, which consists of a flexible tube of plastics material and which is filled with an organic liquid, such a CCl.sub.4, deteriorate with time, since the liquid diffuses out through the plastics flexible tube and/or is decomposed by ultra-violet radiation so that in the flexible tube gas bubbles or products of decomposition are produced, which reduce the transmission of the light guide and therefore the efficiency of the illuminating device to an impermissible extent. Furthermore the light transmission of such previously proposed light guides is highly temperature dependent owing to the substantial differences in the coefficients of thermal expansion of plastics and liquid.
A particular aim of the present invention is that of providing an illuminating device which has the above mentioned, advantageous properties and avoids the above mentioned disadvantages of previously proposed illuminating devices.